JEE Chemistry Biomolecules MCQs Set 07

Answer: (b) native protein

Explanation:
1. A protein with its natural three-dimensional structure and biological activity is called a native protein.

Teacher's Note:
1. Denaturation converts a native protein into a denatured one.
2. The primary sequence is the same in both.

Answer: (b) renaturation

Explanation:
1. Return of a denatured protein to the native state when the agent is removed is renaturation.
2. It shows that the primary structure holds the information for folding.

Teacher's Note:
1. Mild denaturation can be reversed.
2. Boiling an egg is irreversible.

Answer: (b) Prosthetic groups, which get attached to the enzyme only at the time of reaction, are known as cofactors

Explanation:
1. A group attached only during the reaction is a coenzyme, while a prosthetic group is permanently bound.
2. So (b) is not true.
3. Ribozymes are RNA enzymes, and enzymes lower activation energy.

Teacher's Note:
1. Cofactor is the general term for the non-protein part.
2. It covers metal ions, coenzymes and prosthetic groups.

Answer: (c) RNA is the major source of genetic information, which is copied into DNA molecules

Explanation:
1. DNA is the major source of genetic information, which is copied into RNA (transcription).
2. So statement (c) is wrong.

Teacher's Note:
1. The central dogma is DNA to RNA to protein.
2. Retroviruses are the exception.

Answer: (d) all of these

Explanation:
1. Complete hydrolysis gives phosphoric acid, a pentose sugar and nitrogen bases.
2. RNA gives ribose and DNA gives deoxyribose, and both give purines and pyrimidines.

Teacher's Note:
1. Partial hydrolysis gives nucleotides and nucleosides.
2. Complete hydrolysis gives the three components.

Answer: (a) translation

Explanation:
1. The conversion of the m-RNA code into a polypeptide on ribosomes is translation.

Teacher's Note:
1. Transcription is DNA to RNA.
2. Replication is DNA to DNA.

Answer: (b) transcription

Explanation:
1. Making RNA from a DNA template is transcription.
2. RNA polymerase carries it out.

Teacher's Note:
1. Transcription occurs in the nucleus in eukaryotes.
2. Translation takes place at ribosomes.

Answer: (b) it decreases the glucose concentration in the blood

Explanation:
1. Insulin lowers blood glucose by helping cells take up glucose and by promoting glycogen formation.
2. That is why it is hypoglycaemic.

Teacher's Note:
1. Its deficiency causes diabetes.
2. Insulin promotes anabolic processes.

Answer: (a) The C-N bond length in proteins is longer than the usual C-N bond length

Explanation:
1. Lone-pair delocalisation gives the C-N bond partial double-bond character.
2. So it is shorter than a normal C-N single bond, and the group is planar.
3. Statement (a) is incorrect.

Teacher's Note:
1. Delocalisation of the nitrogen lone pair in the amide group restricts rotation.
2. This planarity is important for protein folding.

Answer: (c) Assertion is true but the Reason is false.

Explanation:
1. Teflon is stable and inert because of the very strong C-F bonds.
2. It is a linear polymer, not a cross-linked one, so the reason is false.

Teacher's Note:
1. Teflon is poly(tetrafluoroethene).
2. Its low friction makes it useful for non-stick pans.

Answer: (b) Both Assertion and Reason are true but the Reason is not a correct explanation of the Assertion.

Explanation:
1. Natural rubber has all-cis double bonds in a 1,4-polymer of isoprene, so A is true.
2. Isoprene is indeed 2-methyl-1,3-butadiene, so R is true.
3. R names the monomer but does not explain the cis geometry.

Teacher's Note:
1. Gutta-percha is the all-trans isomer.
2. Cis geometry stops chains packing closely and gives elasticity.

Answer: (d) Both Assertion and Reason are false.

Explanation:
1. Maltose is composed of two glucose units, so A is false.
2. Glucose and galactose differ at C-4, so R is also false.

Teacher's Note:
1. Epimers differ at one stereocentre.
2. Galactose is the C-4 epimer of glucose.

Answer: (b) Both Assertion and Reason are true but the Reason is not a correct explanation of the Assertion.

Explanation:
1. In beta-sheets the chains are almost fully extended, so A is true.
2. Chains are held by hydrogen bonds between neighbouring strands, so R is true.
3. Hydrogen bonding is how the sheet is held but does not itself explain the extended shape.

Teacher's Note:
1. Alpha-helix has intramolecular hydrogen bonds.
2. Beta-sheet has intermolecular hydrogen bonds.

Answer: (d) Both Assertion and Reason are false.

Explanation:
1. Saccharin is about 550 times sweeter than sucrose, so A is false.
2. Saccharin is not a carbohydrate, so R is false.

Teacher's Note:
1. Saccharin is an artificial sweetener.
2. It is excreted unchanged.

Answer: (b) Both Assertion and Reason are true but the Reason is not a correct explanation of the Assertion.

Explanation:
1. Bakelite sets permanently on heating because of cross-linking, so A is true.
2. Its network structure is highly branched, so R is true.
3. The key reason is the cross-links, so R is only a loose description.

Teacher's Note:
1. Thermosetting polymers cannot be remoulded.
2. Thermoplastics soften on heating.

Answer: (d) Both Assertion and Reason are false.

Explanation:
1. Bromine water oxidises only the aldehyde group, giving gluconic acid, so A is false.
2. Bromine water does not oxidise the alcohol groups, so R is false.

Teacher's Note:
1. Nitric acid gives saccharic acid.
2. Bromine water is a mild oxidant.

Answer: (c) Assertion is true but the Reason is false.

Explanation:
1. Non-competitive inhibitors bind at an allosteric site away from the active site and change its shape, so A is true.
2. R is false as they do not bind at the active site.

Teacher's Note:
1. Competitive inhibitors bind at the active site.
2. They resemble the substrate.

Answer: (b) Both Assertion and Reason are true but the Reason is not a correct explanation of the Assertion.

Explanation:
1. RNA is usually single stranded, so A is true.
2. t-RNA carries amino acids, so R is true.
3. The interaction with amino acids is not the reason RNA is single stranded.

Teacher's Note:
1. RNA has ribose and uracil.
2. DNA is double stranded.

Answer: (b) Both Assertion and Reason are true but the Reason is not a correct explanation of the Assertion.

Explanation:
1. Natural rubber is elastic, so A is true.
2. It is a linear polymer, so R is true.
3. Elasticity arises mainly from the coiled cis arrangement and weak forces, not from linearity alone.

Teacher's Note:
1. Vulcanisation cross-links the chains.
2. It improves strength and elasticity.

Answer: (a) Both Assertion and Reason are true and the Reason is a correct explanation of the Assertion.

Explanation:
1. Sucrose has +66.5 degrees and the hydrolysed mixture has a net negative rotation, so A is true.
2. Glucose gives +52.5 degrees and fructose gives -92.4 degrees, so R is true.
3. The larger laevo rotation of fructose is exactly why the mixture is laevorotatory.

Teacher's Note:
1. The mixture is called invert sugar.
2. Honey is largely invert sugar.

Answer: (b) Both Assertion and Reason are true but the Reason is not a correct explanation of the Assertion.

Explanation:
1. Novolac is cross-linked into bakelite on heating with formaldehyde, so A is true.
2. Bakelite is thermosetting and infusible, so R is true.
3. R describes the product and does not explain the reaction.

Teacher's Note:
1. Novolac is the linear, soluble phenol-formaldehyde polymer.
2. The cross-linked product is hard.